This application claims benefit of Japanese Application No. 2000-149673 filed in Japan on May 22, 2000, the contents of which are incorporated by this reference.
1. Field of the Invention
The present invention relates to image display apparatus having a three-dimensionally decentered optical path. More particularly, the present invention relates to a head- or face-mounted image display apparatus that can be retained on an observer""s head or face.
2. Discussion of Related Art
An image display apparatus using a single decentered prism has heretofore been known, for example, in Japanese Patent Application Unexamined Publication (KOKAI) No. Hei 7-333551. The decentered prism has reflecting surfaces arranged to effect two internal reflections. One of the reflecting surfaces is a totally reflecting surface serving as both a reflecting surface and a transmitting surface.
The conventional image display apparatus using the decentered prism suffers, however, from some problems. That is, when the image display device used therein decreases in size, it is necessary to shorten the focal length of the optical system while ensuring the required eye relief. Therefore, it is difficult to construct a viewing optical system of wide field angle.
To solve the above-described problem, the present applicant proposed an image display apparatus in Japanese Patent Application Unexamined Publication (KOKAI) No. 2000-66106, in which a decentered prism similar to the above is disposed on the pupil side, and another decentered prism is disposed on the image display device side.
The above-described arrangement using a combination of two decentered prisms forms a two-dimensionally decentered optical system, and the two decentered prisms have the same decentration plane. Consequently, the image display apparatus is likely to increase in size in the direction of decentration. Therefore, it is difficult to achieve a compact image display apparatus.
Further, an image display apparatus requires various constituent members such as an image display device, a circuit for driving it and an illuminating system in addition to a viewing optical system. With the above-described arrangement, these members cannot effectively be placed in a dead space.
In addition, design is very important for image display apparatus. With the above-described arrangement, the design freedom is limited to a very low degree.
The present invention was made in view of the above-described problems with the prior art.
An object of the present invention is to provide an image display apparatus attaining a reduction in overall size of the apparatus by using an optical system in which all the segments of an axial principal ray extending from a pupil to an image display device are not within the same plane. The image display apparatus further allows various constituent members to be effectively placed in a dead space, thereby permitting the image display apparatus to be designed in a variety of ways.
Another object of the present invention is to provide an image display apparatus favorably corrected for decentration aberrations despite the use of an optical system decentered in a three-dimensional space.
To attain the above-described objects, the present invention provides an image display apparatus having a three-dimensionally decentered optical path. The image display apparatus includes an image display device and a viewing optical system for leading an image formed by the image display device to a pupil corresponding to a position where an observer""s eyeball is to be placed.
The viewing optical system has at least a first reflecting surface and a second reflecting surface positioned closer to the pupil than the first reflecting surface along the optical path. A first plane defined by the optical axis incident on the first reflecting surface and the optical axis reflected therefrom and a second plane defined by the optical axis incident on the second reflecting surface and the optical axis reflected therefrom intersect each other at an arbitrary angle, thereby forming a three-dimensionally decentered optical path. At least either one of the first and second reflecting surfaces has a curved surface configuration.
The reasons for adopting the above-described arrangement in the present invention, together with the function thereof, will be described below.
The image display apparatus according to the present invention includes an image display device and a viewing optical system for leading an image formed by the image display device to a pupil corresponding to a position where an observer""s eyeball is to be placed. The viewing optical system has at least a first reflecting surface and a second reflecting surface disposed closer to the pupil along the optical path. The first reflecting surface corresponds to the surface 24 in Examples (described later). The second reflecting surface corresponds to the surface 22. The optical system is arranged so that a first plane defined by the optical axis incident on the first reflecting surface and the optical axis reflected therefrom and a second plane defined by the optical axis incident on the second reflecting surface and the optical axis reflected therefrom do not extend in the same plane or parallel to each other but intersect each other at an arbitrary angle, whereby the viewing optical system can be decentered three dimensionally. Accordingly, it is possible to fold the optical system in any desired direction and hence possible to reduce the overall size of the image display apparatus. Thus, it is possible to provide an image display apparatus having a minimized dead space in consideration of other associated members. In addition, the degree of design freedom increases favorably.
In a case where a decentered optical system is used as a viewing optical system of a head-mounted image display apparatus, it is desirable with a view to eliminating a dead space and further reducing the overall size of the apparatus to arrange the optical system so that a first plane defined by the optical axis incident on the first reflecting surface and the optical axis reflected therefrom and a second plane defined by the optical axis incident on the second reflecting surface and the optical axis reflected therefrom intersect each other at an arbitrary angle, as stated above. In such a case, the optical system must inevitably be decentered three dimensionally, and this causes rotationally asymmetric aberrations to occur. It is impossible to correct the rotationally asymmetric aberrations by only a rotationally symmetric optical system. The best surface configuration for correcting the rotationally asymmetric aberrations due to three-dimensional decentration is a rotationally asymmetric surface. Therefore, in the image display apparatus according to the present invention, it is desirable that at least either one of the first and second reflecting surfaces should have a rotationally asymmetric curved surface configuration that corrects decentration aberrations.
It is preferable that the viewing optical system should have at least one reflecting surface in addition to the first and second reflecting surfaces, i.e. reflecting surfaces corresponding to the surfaces 12, 13, 22, 23 and 24 in Examples (described later), and at least two of the plurality of reflecting surfaces should have a rotationally asymmetric curved surface configuration that corrects decentration aberrations.
In the present invention, a free-form surface is used as a typical example of a surface having a rotationally asymmetric curved surface configuration. A free-form surface is defined by the following equation. The Z-axis of the defining equation is the axis of a free-form surface.                     Z        =                                            cr              2                        /                          [                              1                +                                                      {                                          1                      -                                                                        (                                                      1                            +                            k                                                    )                                                ⁢                                                  c                          2                                                ⁢                                                  r                          2                                                                                      }                                                              ]                                +                                    ∑                              j                =                2                            66                        ⁢                          xe2x80x83                        ⁢                                          C                j                            ⁢                              X                m                            ⁢                              Y                n                                                                        (        a        )            
In the equation (a), the first term is a spherical surface term, and the second term is a free-form surface term.
In the spherical surface term:
c: the curvature at the vertex
k: a conic constant
r={square root over ( )} (X2+Y2)
The free-form surface term is given by                                           ∑                          j              =              2                        66                    ⁢                      xe2x80x83                    ⁢                                    C              j                        ⁢                          X              m                        ⁢                          Y              n                                      =                  xe2x80x83                ⁢                                            C              2                        ⁢            X                    +                                    C              3                        ⁢            Y                    +                                    C              4                        ⁢                          X              2                                +                                    C              5                        ⁢            XY                    +                                    C              6                        ⁢                          Y              2                                +                                                  xe2x80x83                ⁢                                            C              7                        ⁢                          X              3                                +                                    C              8                        ⁢                          X              2                        ⁢            Y                    +                                    C              9                        ⁢                          XY              2                                +                                    C              10                        ⁢                          Y              3                                +                                    C              11                        ⁢                          X              4                                +                                                  xe2x80x83                ⁢                                            C              12                        ⁢                          X              3                        ⁢            Y                    +                                    C              13                        ⁢                          X              2                        ⁢                          Y              2                                +                                    C              14                        ⁢                          XY              3                                +                                    C              15                        ⁢                          Y              4                                +                                                  xe2x80x83                ⁢                                            C              16                        ⁢                          X              5                                +                                    C              17                        ⁢                          X              4                        ⁢            Y                    +                                    C              18                        ⁢                          X              3                        ⁢                          Y              2                                +                                    C              19                        ⁢                          X              2                        ⁢                          Y              3                                +                                                  xe2x80x83                ⁢                                            C              20                        ⁢                          XY              4                                +                                    C              21                        ⁢                          Y              5                                +                                    C              22                        ⁢                          X              6                                +                                    C              23                        ⁢                          X              5                        ⁢            Y                    +                                                  xe2x80x83                ⁢                                            C              24                        ⁢                          X              4                        ⁢                          Y              2                                +                                    C              25                        ⁢                          X              3                        ⁢                          Y              3                                +                                    C              26                        ⁢                          X              2                        ⁢                          Y              4                                +                                    C              27                        ⁢                          XY              5                                +                                                  xe2x80x83                ⁢                                            C              28                        ⁢                          Y              6                                +                                    C              29                        ⁢                          X              7                                +                                    C              30                        ⁢                          X              6                        ⁢            Y                    +                                    C              31                        ⁢                          X              5                        ⁢                          Y              2                                +                                                  xe2x80x83                ⁢                                            C              32                        ⁢                          X              4                        ⁢                          Y              3                                +                                    C              33                        ⁢                          X              3                        ⁢                          Y              4                                +                                    C              34                        ⁢                          X              2                        ⁢                          Y              5                                +                                    C              35                        ⁢                          XY              6                                +                                                  xe2x80x83                ⁢                              C            36                    ⁢                      Y            7                    ⁢                      xe2x80x83                    ⁢          …                    
where Cj (j is an integer of 2 or higher) are coefficients.
In general, the above-described free-form surface does not have planes of symmetry in both the XZ- and YZ-planes. However, a free-form surface having only one plane of symmetry parallel to the YZ-plane is obtained by making all terms of odd-numbered degrees with respect to X zero. A free-form surface having only one plane of symmetry parallel to the XZ-plane is obtained by making all terms of odd-numbered degrees with respect to Y zero.
In addition, free-form surfaces as the above-described surfaces with a rotationally asymmetric curved surface configuration may be defined by Zernike polynomials. That is, the configuration of a free-form surface may be defined by the following equation (b). The Z-axis of the defining equation (b) is the axis of Zernike polynomial. A rotationally asymmetric surface is defined by polar coordinates of the height of the Z-axis with respect to the XY-plane. In the equation (b), A is the distance from the Z-axis in the XY-plane, and R is the azimuth angle about the Z-axis, which is expressed by the angle of rotation measured from the Z-axis.                                                         x              =                              xe2x80x83                            ⁢                              R                xc3x97                                  cos                  ⁡                                      (                    A                    )                                                                                                                          y              =                              xe2x80x83                            ⁢                              R                xc3x97                                  sin                  ⁡                                      (                    A                    )                                                                                                                          Z              =                              xe2x80x83                            ⁢                                                D                  2                                +                                                      D                    3                                    ⁢                  R                  ⁢                                      xe2x80x83                                    ⁢                                      cos                    ⁡                                          (                      A                      )                                                                      +                                                      D                    4                                    ⁢                  R                  ⁢                                      xe2x80x83                                    ⁢                                      sin                    ⁡                                          (                      A                      )                                                                      +                                                      D                    5                                    ⁢                                      R                    2                                    ⁢                                      cos                    ⁡                                          (                                              2                        ⁢                        A                                            )                                                                      +                                                                                                        xe2x80x83                            ⁢                                                                    D                    6                                    ⁡                                      (                                                                  R                        2                                            -                      1                                        )                                                  +                                                      D                    7                                    ⁢                                      R                    2                                    ⁢                                      sin                    ⁡                                          (                                              2                        ⁢                        A                                            )                                                                      +                                                      D                    8                                    ⁢                                      R                    3                                    ⁢                                      cos                    ⁡                                          (                                              3                        ⁢                        A                                            )                                                                      +                                                                                                        xe2x80x83                            ⁢                                                                                          D                      9                                        ⁡                                          (                                                                        3                          ⁢                                                      R                            3                                                                          -                                                  2                          ⁢                          R                                                                    )                                                        ⁢                                      cos                    ⁡                                          (                      A                      )                                                                      +                                                                            D                      10                                        ⁡                                          (                                                                        3                          ⁢                                                      R                            3                                                                          -                                                  2                          ⁢                          R                                                                    )                                                        ⁢                                      sin                    ⁡                                          (                      A                      )                                                                      +                                                                                                        xe2x80x83                            ⁢                                                                    D                    11                                    ⁢                                      R                    3                                    ⁢                                      sin                    ⁡                                          (                                              3                        ⁢                        A                                            )                                                                      +                                                      D                    12                                    ⁢                                      R                    4                                    ⁢                                      cos                    ⁡                                          (                                              4                        ⁢                        A                                            )                                                                      +                                                                            D                      13                                        ⁡                                          (                                                                        4                          ⁢                                                      R                            4                                                                          -                                                  3                          ⁢                                                      R                            2                                                                                              )                                                        ⁢                                      cos                    ⁡                                          (                                              2                        ⁢                        A                                            )                                                                      +                                                                                                        xe2x80x83                            ⁢                                                                    D                    14                                    ⁡                                      (                                                                  6                        ⁢                                                  R                          4                                                                    -                                              6                        ⁢                                                  R                          2                                                                    +                      1                                        )                                                  +                                                                            D                      15                                        ⁡                                          (                                                                        4                          ⁢                                                      R                            4                                                                          -                                                  3                          ⁢                                                      R                            2                                                                                              )                                                        ⁢                                      sin                    ⁡                                          (                                              2                        ⁢                        A                                            )                                                                      +                                                                                                        xe2x80x83                            ⁢                                                                    D                    16                                    ⁢                                      R                    4                                    ⁢                                      sin                    ⁡                                          (                                              4                        ⁢                        A                                            )                                                                      +                                                      D                    17                                    ⁢                                      R                    5                                    ⁢                                      cos                    ⁡                                          (                                              5                        ⁢                        A                                            )                                                                      +                                                                            D                      18                                        ⁡                                          (                                                                        5                          ⁢                                                      R                            5                                                                          -                                                  4                          ⁢                                                      R                            3                                                                                              )                                                        ⁢                                      cos                    ⁡                                          (                                              3                        ⁢                        A                                            )                                                                      +                                                                                                        xe2x80x83                            ⁢                                                                                          D                      19                                        ⁡                                          (                                                                        10                          ⁢                                                      R                            5                                                                          -                                                  12                          ⁢                                                      R                            3                                                                          +                                                  3                          ⁢                          R                                                                    )                                                        ⁢                                      cos                    ⁡                                          (                      A                      )                                                                      +                                                                                                        xe2x80x83                            ⁢                                                                                          D                      20                                        ⁡                                          (                                                                        10                          ⁢                                                      R                            5                                                                          -                                                  12                          ⁢                                                      R                            3                                                                          +                                                  3                          ⁢                          R                                                                    )                                                        ⁢                                      sin                    ⁡                                          (                      A                      )                                                                      +                                                                            D                      21                                        ⁡                                          (                                                                        5                          ⁢                                                      R                            5                                                                          -                                                  4                          ⁢                                                      R                            3                                                                                              )                                                        ⁢                                      sin                    ⁡                                          (                                              3                        ⁢                        A                                            )                                                                      +                                                                                                        xe2x80x83                            ⁢                                                                    D                    22                                    ⁢                                      R                    5                                    ⁢                                      sin                    ⁡                                          (                                              5                        ⁢                        A                                            )                                                                      +                                                      D                    23                                    ⁢                                      R                    6                                    ⁢                                      cos                    ⁡                                          (                                              6                        ⁢                        A                                            )                                                                      +                                                                            D                      24                                        ⁡                                          (                                                                        6                          ⁢                                                      R                            6                                                                          -                                                  5                          ⁢                                                      R                            4                                                                                              )                                                        ⁢                                      cos                    ⁡                                          (                                              4                        ⁢                        A                                            )                                                                      +                                                                                                        xe2x80x83                            ⁢                                                                                          D                      25                                        ⁡                                          (                                                                        15                          ⁢                                                      R                            6                                                                          -                                                  20                          ⁢                                                      R                            4                                                                          +                                                  6                          ⁢                                                      R                            2                                                                                              )                                                        ⁢                                      cos                    ⁡                                          (                                              2                        ⁢                        A                                            )                                                                      +                                                                                                        xe2x80x83                            ⁢                                                                    D                    26                                    ⁡                                      (                                                                  20                        ⁢                                                  R                          6                                                                    -                                              30                        ⁢                                                  R                          4                                                                    +                                              12                        ⁢                                                  R                          2                                                                    -                      1                                        )                                                  +                                                                                                        xe2x80x83                            ⁢                                                                                          D                      27                                        ⁡                                          (                                                                        15                          ⁢                                                      R                            6                                                                          -                                                  20                          ⁢                                                      R                            4                                                                          +                                                  6                          ⁢                                                      R                            2                                                                                              )                                                        ⁢                                      sin                    ⁡                                          (                                              2                        ⁢                        A                                            )                                                                      +                                                                                                        xe2x80x83                            ⁢                                                                                          D                      28                                        ⁡                                          (                                                                        6                          ⁢                                                      R                            6                                                                          -                                                  5                          ⁢                                                      R                            4                                                                                              )                                                        ⁢                                      sin                    ⁡                                          (                                              4                        ⁢                        A                                            )                                                                      +                                                      D                    29                                    ⁢                                      R                    6                                    ⁢                                      sin                    ⁡                                          (                                              6                        ⁢                        A                                            )                                                        ⁢                                      xe2x80x83                                    ⁢                  …                                                                                        (        b        )            
where Dm (m is an integer of 2 or higher) are coefficients. It should be noted that to design an optical system symmetric with respect to the X-axis direction, D4, D5, D6, D10, D11, D12, D13, D14, D20, D21, D22 . . . should be used.
The above defining equations are shown to exemplify surfaces with a rotationally asymmetric curved surface configuration. Therefore, the same advantageous effects can be obtained for any other defining equation that expresses such a rotationally asymmetric surface.
It should be noted that other examples of defining equations for free-form surfaces include the following defining equation (c):
Z=xcexa3xcexa3CnmXY
Assuming that k=7 (polynomial of degree 7), for example, a free-form surface is expressed by an expanded form of the above equation as follows:                                                         Z              =                              xe2x80x83                            ⁢                                                C                  2                                +                                                      C                    3                                    ⁢                  Y                                +                                                      C                    4                                    ⁢                                      "LeftBracketingBar"                    X                    "RightBracketingBar"                                                  +                                                      C                    5                                    ⁢                                      Y                    2                                                  +                                                      C                    6                                    ⁢                  Y                  ⁢                                      "LeftBracketingBar"                    X                    "RightBracketingBar"                                                  +                                                      C                    7                                    ⁢                                      X                    2                                                  +                                                                                                        xe2x80x83                            ⁢                                                                    C                    8                                    ⁢                                      Y                    3                                                  +                                                      C                    9                                    ⁢                                      Y                    2                                    ⁢                                      "LeftBracketingBar"                    X                    "RightBracketingBar"                                                  +                                                      C                    10                                    ⁢                                      YX                    2                                                  +                                                      C                    11                                    ⁢                                      "LeftBracketingBar"                                          X                      3                                        "RightBracketingBar"                                                  +                                                      C                    12                                    ⁢                                      Y                    4                                                  +                                                                                                        xe2x80x83                            ⁢                                                                    C                    13                                    ⁢                                      Y                    3                                    ⁢                                      "LeftBracketingBar"                    X                    "RightBracketingBar"                                                  +                                                      C                    14                                    ⁢                                      Y                    2                                    ⁢                                      X                    2                                                  +                                                      C                    15                                    ⁢                  Y                  ⁢                                      "LeftBracketingBar"                                          X                      3                                        "RightBracketingBar"                                                  +                                                      C                    16                                    ⁢                                      X                    4                                                  +                                                                                                        xe2x80x83                            ⁢                                                                    C                    17                                    ⁢                                      Y                    5                                                  +                                                      C                    18                                    ⁢                                      Y                    4                                    ⁢                                      "LeftBracketingBar"                    X                    "RightBracketingBar"                                                  +                                                      C                    19                                    ⁢                                      Y                    3                                    ⁢                                      X                    2                                                  +                                                      C                    20                                    ⁢                                      Y                    2                                    ⁢                                      "LeftBracketingBar"                                          X                      3                                        "RightBracketingBar"                                                  +                                                      C                    21                                    ⁢                                      YX                    4                                                  +                                                                                                        xe2x80x83                            ⁢                                                                    C                    22                                    ⁢                                      "LeftBracketingBar"                                          X                      5                                        "RightBracketingBar"                                                  +                                                      C                    23                                    ⁢                                      Y                    6                                                  +                                                      C                    24                                    ⁢                                      Y                    5                                    ⁢                                      "LeftBracketingBar"                                          X                      ⁢                                              "LeftBracketingBar"                                                                                                            +                                                              C                                25                                                                                      ⁢                                                          Y                              4                                                        ⁢                                                          X                              2                                                                                +                                                                                    C                              26                                                        ⁢                                                          Y                              3                                                        ⁢                                                          "LeftBracketingBar"                                                              X                                3                                                            "RightBracketingBar"                                                                                +                                                                                                                                                                                                            xe2x80x83                            ⁢                                                                    C                    27                                    ⁢                                      Y                    2                                    ⁢                                      X                    4                                                  +                                                      C                    28                                    ⁢                  Y                  ⁢                                      "LeftBracketingBar"                                          X                      5                                        "RightBracketingBar"                                                  +                                                      C                    29                                    ⁢                                      X                    6                                                  +                                                      C                    30                                    ⁢                                      Y                    7                                                  +                                                      C                    31                                    ⁢                                      Y                    6                                    ⁢                                      "LeftBracketingBar"                    X                    "RightBracketingBar"                                                  +                                                                                                        xe2x80x83                            ⁢                                                                    C                    32                                    ⁢                                      Y                    5                                    ⁢                                      X                    2                                                  +                                                      C                    33                                    ⁢                                      Y                    4                                    ⁢                                      "LeftBracketingBar"                                          X                      3                                        "RightBracketingBar"                                                  +                                                      C                    34                                    ⁢                                      Y                    3                                    ⁢                                      X                    4                                                  +                                                      C                    35                                    ⁢                                      Y                    2                                    ⁢                                      "LeftBracketingBar"                                          X                      5                                        "RightBracketingBar"                                                  +                                                                                                        xe2x80x83                            ⁢                                                                    C                    36                                    ⁢                                      YX                    6                                                  +                                                      C                    37                                    ⁢                                      "LeftBracketingBar"                                          X                      7                                        "RightBracketingBar"                                                                                                          (        c        )            
It should be noted that an anamorphic surface or a toric surface is also usable as a surface having a rotationally asymmetric curved surface configuration.
The viewing optical system may be formed from a prism member. The prism member may have at least the first and second reflecting surfaces provided on prism surfaces, together with a first transmitting surface through which a display light beam from the image display device enters the prism member, and a second transmitting surface through which the display light beam exits the prism member toward the pupil. The prism member corresponds to a combination of an ocular prism and an optical path distributing prism that are integrated into a single prism member or separate from each other in Examples (described later).
In this case, it is desirable that the prism member should have at least one reflecting surface closer to the pupil than the second reflecting surface, and this reflecting surface should have a rotationally asymmetric curved surface configuration that corrects decentration aberrations.
It is preferable that the prism member should have a third reflecting surface and a fourth reflecting surface closer to the pupil than the second reflecting surface, and a third plane defined by the optical axis incident on the third reflecting surface and the optical axis reflected therefrom should intersect the second plane defined with respect to the second reflecting surface at an angle, and further a fourth plane defined by the optical axis incident on the fourth reflecting surface and the optical axis reflected therefrom should be in the same plane as the third plane, and further at least either one of the third and fourth reflecting surfaces should have a rotationally asymmetric curved surface configuration that corrects decentration aberrations. All of Examples (described later) have an arrangement corresponding to the above-described arrangement of the prism member.
In this case, it is desirable that both the third and fourth reflecting surfaces should have a rotationally asymmetric curved surface configuration that corrects decentration aberrations.
It is preferable to arrange the prism member so that a light beam is incident on the second transmitting surface at an angle exceeding the total reflection critical angle, thereby allowing the second transmitting surface to serve also as the third reflecting surface. In other words, the third reflecting surface is formed from the identical surface with the second transmitting surface. Thus, the light beam reflected by the totally reflecting action of the third reflecting surface is reflected by the fourth reflecting surface, and the light beam reflected from the fourth reflecting surface passes through the second transmitting surface to exit the prism member. All of Examples (described later) have an arrangement corresponding to the above-described arrangement of the prism member.
It is preferable that the prism member should have a plurality of reflecting surfaces, including the first reflecting surface, in the optical path between the first transmitting surface and the second reflecting surface, and at least one of the plurality of reflecting surfaces, exclusive of the first reflecting surface, should have a rotationally asymmetric curved surface configuration that corrects decentration aberrations. The optical path distributing prism in Examples (described later) has an arrangement corresponding to the above-described arrangement of the prism member.
The prism member may have the first reflecting surface and a fifth reflecting surface in the order mentioned along the optical path between the first transmitting surface and the second reflecting surface. In this case, a fifth plane defined by the optical axis incident on the fifth reflecting surface and the optical axis reflected therefrom is in the same plane as the first plane defined with respect to the first reflecting surface. All of Examples (described later) have an arrangement corresponding to the above-described arrangement of the prism member.
In this case, the prism member may be arranged as follows. The first reflecting surface is provided on a surface of the prism member at a tilt so as to reflect the light beam entering through the first transmitting surface toward a position closer to the second reflecting surface than the direction of incidence of the light beam. The fifth reflecting surface is provided on a surface of the prism member at a tilt so as to reflect the light beam reflected from the first reflecting surface toward a position closer to the second reflecting surface than the direction of incidence of the light beam. Examples 1 and 2 (described later) have an arrangement corresponding to the above-described arrangement of the prism member.
Further, the prism member may be arranged as follows. The first reflecting surface is provided on a surface of the prism member at a tilt so as to reflect the light beam entering through the first transmitting surface toward a position more away from the second reflecting surface than the direction of incidence of the light beam. The fifth reflecting surface is provided on a surface of the prism member at a tilt so as to reflect the light beam reflected from the first reflecting surface toward a position closer to the second reflecting surface than the direction of incidence of the light beam. Thus, the prism member is arranged so that an optical path connecting the first transmitting surface and the first reflecting surface and an optical path connecting the fifth reflecting surface and the second reflecting surface intersect each other within the prism member. Examples 3 and 4 (described later) have an arrangement corresponding to the above-described arrangement of the prism member.
The prism member may have a first prism and a second prism that are separated by at least an air layer. In this case, the first prism has at least the first reflecting surface and the second reflecting surface and forms a three-dimensionally decentered optical path. All of Examples (described later) have an arrangement corresponding to the above-described arrangement of the prism member.
In this case, the first prism may have a first prism exit surface through which the light beam reflected from the second reflecting surface exits the first prism toward the second prism. In this arrangement, there is no reflecting surface between the second reflecting surface and the first prism exit surface. All of Examples (described later) have an arrangement corresponding to the above-described arrangement of the prism member.
It is desirable that the prism member should have a first prism and a second prism that are separated by at least an air layer, and an exit surface of the first prism that faces the second prism across the air layer should have a rotationally asymmetric curved surface configuration that corrects decentration aberrations.
It is also desirable that the prism member should have a first prism and a second prism that are separated by at least an air layer, and an entrance surface of the second prism that faces the first prism across the air layer should have a rotationally asymmetric curved surface configuration that corrects decentration aberrations.
The first transmitting surface should preferably have a rotationally asymmetric curved surface configuration that corrects decentration aberrations.
It is also preferable that the second transmitting surface should have a rotationally asymmetric curved surface configuration that corrects decentration aberrations.
The viewing optical system should preferably be arranged to form the image of the image display device as an intermediate image in the vicinity of the second reflecting surface and to lead the intermediate image to the pupil. All of Examples (described later) have an arrangement corresponding to the above-described arrangement of the viewing optical system.
In this case, the viewing optical system should preferably be arranged to form the intermediate image at a position closer to the pupil than the second reflecting surface.
The above-described rotationally asymmetric curved surface configuration that corrects decentration aberrations should preferably be formed from a rotationally asymmetric aspherical surface having not more than two planes of symmetry. The rotationally asymmetric aspherical surface should preferably be a free-form surface having only one plane of symmetry.
The present invention also includes an image pickup apparatus in which an image pickup device is provided in place of the image display device in the above-described arrangement. In this case, the pupil is arranged as an entrance pupil through which a light beam from a subject passes, and the viewing optical system is used as an image-forming optical system that focuses the light beam from the subject to form a subject image on the image pickup device.
Further, the present invention includes a projection apparatus in which a projection image plane is provided in place of the image display device in the foregoing arrangement. When a screen is placed in front of the pupil, the viewing optical system is used as a projection optical system that projects a light beam from the projection image plane onto the screen as a projected image.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.